U.S. Pat. No. 4,528,848 discloses an apparatus for continuous gravimetric metering of pourable material conveyed through a charging inlet into pockets of a rotor arranged in a housing rotatable about an essentially vertical axis and fed out from the pockets through a discharging outlet arranged offset in respect of the charging inlet in rotational direction of the rotor. The housing is mounted in a frame pivotally about an essentially horizontal axis and depends on the frame via a load cell arranged remote from said axis. Pressurized air is supplied through an opening provided opposite the discharging outlet. Elastic connecting elements as compensators flexibly couple said housing to corresponding ducts for charging and discharging the material and for supplying pressurized air.
Such a gravimetric metering apparatus operates with high satisfaction even on a long term basis. However, due to the pneumatic conveying it must have a very stable and rigid design which is of particular disadvantage when conveying high quantities of pourable material. Furthermore, there are some problems when conveying pourable material which tend to stick together such as powdered cement.
Typically, with a known system such powdered cement is supplied to a heat exchanger from a bin in metered large quantities as 100 to 300 tons per hour. For such purpose the material is guided through a conveyor trough onto a belt-type metering device. The conveyor trough is arranged in an inclined position and is provided with a porous bottom permitting air being finely distributed from a pressurized air space into the material conveyed on the conveyor trough. However, such a system operates as an open system which requires considerable measures as covers and enclosures in order to comply with environmental regulations.
German Laid Open Patent Publication 1,010,014 relates to a device for pneumatically emptying a container from powdered material. There is provided a type of syphon having a porous bottom through which air is blown from a pressurized air space into the syphon for causing the material to be mixed with the air to form a dust-air mixture.
The German Laid Open Patent Publication 3,901,772 relates to a weighing apparatus having a weighing container eccentrically depending from a load cell. Since the outlet portion is curvedly formed, no closing element is necessary but the material is selfblocking and is suctioned out when desired.
The German Patent Specification 2,234,134 relates to a pneumatic conveying system using a level determining element for controlling the level in a container.
The German published Patent Application 2,021,493 relates to a conveyor trough for pneumatic conveying of pourable material. Between an upper box and a lower box there is arranged an air permeable wall.